Environments around abnormal cells such as cancer cells are known to be weakly acidic with a pH of 6.0 to 7.2, unlike the normal body environment which ranges in pH from 7.2 to 7.4. Therapies for cancer using this property are under study.
Korean Patent No. 802080, issued to the Sungkyunkwan University Foundation for Corporate Collaboration, discloses a pH-sensitive copolymer consisting of biodegradable poly(β-aminoester) and hydrophilic polyethylene glycol, which can form micelle structures due to their own amphiphilicity and pH-dependent ionization, whereby the micelles can deliver drugs to cancer cells depending on the change in pH and kill the cells.
WO 2002/20510 discloses novel acid-sensitive compounds comprising an acid-sensitive cyclic ortho-ester and at least one hydrophilic substituent, and their salts. The compounds form conjugates (liposomes, complexes, nanoparticles, etc.) with therapeutic molecules so as to release the therapeutic molecule in cell tissues or compartments where the pH thereof is acidic.
Plasmons play a large role in the optical properties of metals. Surface plasmons are the collective oscillations of free electrons of a metal surface on which light is incident, which take place due to resonance with electromagnetic waves of specific energy that propagate in a direction parallel to the metal/dielectric (e.g., air, water) interface. Because the interactions between light and metal nanoparticles are so strong, the metal nanoparticles show very large coefficients of absorption at resonant frequencies compared to organic dyes. In addition, the resonant frequency of metal nanoparticles varies depending on various factors including size, morphology, kinds of solvents in which they are suspended, etc. Thus, a lot of efforts have been being made into applying various metal nanoparticles to optical sensors or condensers by modifying them in terms of size, morphology, and surface properties.
Recently, metal nanoparticles have been becoming popular because of the possibility of their being used in photothermal therapy thanks to the light-harvesting effect thereof. Photothermal therapy is a use of light energy in the form of thermal energy and is used to treat various medical conditions, including cancer. The light collected on the surface of gold nanoparticles is emitted by various processes, including electron-lattice vibrations, and electron-electron scattering, with the concomitant production of heat. In consideration of the great light-harvesting effect and large surface area-to-volume of gold nanoparticles, the thermal energy locally emitted from the gold nanoparticles is sufficient to cause cell death. Further, because cancer cells are highly vulnerable to heat compared to normal cells, the heat emitted from gold nanoparticles on which light is focused at a controlled intensity can be locally introduced to selectively kill cancer cells without damaging normal cells.
Korean Patent Application No. 2006-102604 discloses a core-shell particle consisting of a silica core 50-500 nm in size, and a gold shell embedded with magnetic nanoparticles, with cancer cell-targeting ligands bonded to the gold shell. The core-shell particle is useful for the diagnosis and magnetic resonance imaging of cancer by taking advantage of the magnetic nanoparticles attached to cancer cells via the cancer cell-targeting ligands. Further, the heat released from the gold nanoshell absorbing the energy of electromagnetic pulses in the near infrared ray range can be used to selectively destroy cancer cells. However, problems with the core-shell particle structure include that of the development of biological ligands for effectively detecting specific cancer cells and conjugating them to the metal.
There is therefore a need for metal nanoparticles that can selectively detect various cancer cells.